Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Bibliography: leaves 110-115.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.S.)--University of Akron, Dept. of Mechanical Engineering, 2009. / "May, 2009." Title from electronic thesis title page (viewed 8/2/2009) Advisor, Celal Batur; Co-advisor, Ali Sayir; Committee member, Jiang Zhe; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on June 9, 2009) Vita. Includes bibliographical references.

Two types of devices employing ferroelectric modulation of a semiconductor thin-film have been realized and studied. The first consists of a cadmium selenide film with electrodes deposited on a barium titanate substrate together with a switching electrode on the other side of the substrate. This gives a two-valued resistor; in effect, a nondestructive readout of the state of the ferroelectric crystal which is regarded as a storage element. The second device is a thin-film transistor (TFT) deposited on a barium titanate crystal. A fourth counterelectrode - on the other side of the crystal allows changing between two opposite polarization directions in the crystal, thus giving a TFT with two sets of characteristics, roughly equivalent to a two-valued built-in gate bias. The read-in, or switching time, of the device is substantially determined by the barium titanate crystal and can be in the microsecond range for high switching fields. Readout of the devices can be continuous or not, as desired. Characteristics of the TFT, which is considered equivalent to a two-gate device, are analyzed in terms of the gradual channel approximation. Experimental results of the two devices are presented and discussed in relation to the predicted behaviour. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

With the projected growth of the flexible and plastic electronics industry, there is renewed interest in the research community to develop high performance all-polymeric memory which will be an essential component of any electronic circuit. Some of the efforts in polymer memories are based on different mechanisms such as filamentary conduction, charge trapping effects, dipole alignment, and reduction-oxidation to name a few. Among these the leading candidate are those based on the mechanism of ferroelectricity. Polymer ferroelectric memory can be used in niche applications like smart cards, RFID tags, sensors etc. This dissertation will focus on novel material and device engineering to fabricate high performance low temperature polymeric ferroelectric memory for flexible electronics. We address and find solutions to some fundamental problems affecting all polymer ferroelectric memory like high coercive fields, fatigue and thermal stability issues, poor breakdown strength and poor p-type hole mobilities. Some of the strategies adopted in this dissertation are: Use of different flexible substrates, electrode engineering to improve charge injection and fatigue properties of ferroelectric polymers, large area ink jet printing of ferroelectric memory devices, use of polymer blends to improve insulating properties of ferroelectric polymers and use of oxide semiconductors to fabricate high mobility p-type ferroelectric memory. During the course of this dissertation we have fabricated: the first all-polymer ferroelectric capacitors with solvent modified highly conducting polymeric poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) [PEDOT:PSS] electrodes on plastic substrates with performance as good as devices with metallic Platinum-Gold electrodes on silicon substrates; the first all-polymer high performance ferroelectric memory on banknotes for security applications; novel ferroelectric capacitors based on blends of ferroelectric poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] and highly insulating dielectric poly(p-phenylene oxide) [PPO] with drastically improved fatigue and thermal stability; novel all-polymer ferroelectric diodes based on blends of ferroelectric [P(VDF-TrFE)] and n-type semiconducting [6,6]-phenyl-C61-butyric acid methyl ester [PCBM] with resistive switching properties and the first hybrid p-type ferroelectric memory with transparent tin monoxide [SnO] on plastic substrates with record mobilities.

No description available.

Piezoelectric materials find applications in number of devices requiring inter-conversion of mechanical and electrical energy.  These devices include different types of sensors, actuators and energy harvesting devices. A number of lead-based perovskite compositions (PZT, PMN-PT, PZN-PT etc.) have dominated the field in last few decades owing to their giant piezoresponse and convenient application relevant tunability. With increasing environmental concerns, in the last one decade, focus has been shifted towards developing a better understanding of lead-free piezoelectric compositions in order to achieve an improved application relevant performance.  Sodium potassium niobate (KxNa1-xNbO3, abbreviated as KNN) is one of the most interesting candidates in the class of lead-free piezoelectrics. Absence of any poisonous element makes it unique among all the other lead-free candidates having presence of bismuth. Curie temperature of 400"C, even higher than that of PZT is another advantage from the point of view of device applications. Present work focuses on the development of fundamental understanding of the crystallographic nature, domain structure and domain dynamics of KNN. Since compositions close to x = 0.5 are of primary interest because of their superior piezoelectric activity among other compositions (0 < x < 1), crystallographic and domain structure studies are focused on this region of the phase diagram. KNN random ceramic, textured ceramic and single crystals were synthesized, which in complement to each other help in understanding the behavior of KNN. K0.5Na0.5NbO3 single crystals grown by the flux method were characterized for their ferroelectric and piezoelectric behavior and dynamical scaling analysis was performed to reveal the origin of their moderate piezoelectric performance. Optical birefringence technique used to reveal the macro level crystallographic nature of x = 0.4, 0.5 and 0.6 crystals suggested them to have monoclinic Mc, monoclinic MA/B and orthorhombic structures respectively. Contrary to that, pair distribution function analysis performed on same composition crystals implies them to belonging to monoclinic Mc structure at local scale. Linear birefringence and piezoresponse force microscopy (PFM) were used to reveal the domain structure at macro and micros scales respectively. A noble sintering technique was developed to achieve > 99% density for KNN ceramics. These high density ceramics were characterized for their dielectric, ferroelectric and piezoelectric properties. A significant improvement in different piezoelectric coefficients of these ceramics validates the advantages of this sintering technique. Also lower defect levels in these high density ceramics lead to the superior ferroelectric fatigue behavior as well. To understand the role of seed crystals in switching behavior of textured ceramic, highly textured KNN ceramics (Lotgering factor ~ 88 %) were synthesized using TGG method. A sintering technique similar to one employed for random ceramics, was used to sinter textured KNN ceramics as well. Piezoresponse force microscopy (PFM) study suggested these textured ceramics to have about 6¼m domains as compared to 2¼m domain size for random ceramics.  Local switching behavior studied using switching spectroscopy (SS-PFM) revealed about two and half time improvement of local piezoresponse as compared to random counterpart. / Ph. D.

In recent years bismuth-based, layer-structured perovskites such as SrBi2Nb2O9 (SBN) and SrBi2Ta2O9 (SBT) have been investigated extensively, because of their potential use in ferroelectric random access memories (FeRAMs). In comparison with non-layered perovskite ferroelectrics such as Pb(Zr,Ti)O3 (PZT), these offer several advantages such as fatigue free, lead free, low operating voltages and most importantly their ferroelectric properties are independent of film thickness in the 90 to 500 nm range. For FeRAM device applications, large remnant polarization (Pr), low coercive field (Ec) accompanied by high Curie temperature (Tc) are required for better performance and reliable operation. Much effort has been made to improve the ferroelectric properties of SBN and SBT ceramics by doping on A or B sites. It was known in the literature that partial substitution of Sr2+ by Bi3+ ions in SBN and SBT would increase the Curie temperature and improve the dielectric properties. The focus of the investigations that were taken up was to improve the electrical, dielectric and ferroelectric characteristics of SrBi2Nb2O9 ceramics. It was reported that the ferroelectric and nonlinear optical properties of LiNbO3 and LiTaO3 could be improved when vanadium, the lightest element in group V of the periodic table is substituted for Nb or Ta along with Li and three oxygens. It is with this background the investigations have been taken up to see whether one can extend the same argument to the Aurivillius family of oxides. Therefore, the central theme of the present investigations aimed at substituting Nb5+ by a smaller cation V5+ in SBN and study its influence on the formation temperature, sinterability, structural and microstructural characteristics apart from its physical properties. Recently the optical properties of this material have been recognized to be important from the optical device point of view. Unfortunately single crystal growth of vanadium doped SBN was hampered because of the bismuth and vanadium loss (high volatility) observed in the process of growth. One of the routes that attracted our attention has been the glass-ceramic. It would be interesting to visualize the behavior of crystallites of nano/micrometer size embedded in a glass matrix as these crystals were known to give rise to exotic properties. One of the crucial steps in the process of fabrication of a glass nanocrystalcomposite system in which crystalline phases have symmetries that would eventually give rise to basic non - centrosymmetric properties such as piezoelectric, pyroelectric and Pockels effects, has been to choose a compatible matrix material associated with easy glass forming capability and the ability to evenly disperse dipolar defects within itself. Recent investigations into strontium borate SrB4O7 (SBO), lithium borate Li2B4O7 (LBO) glasses indicated that LBO by virtue of its favorable structure, thermal and optical properties would form a suitable host glass matrix for dispersing layer structured ferroelectric oxides belonging to the Aurivillius family of oxides. Since lithium borate has wide transmission window, it was worth making an attempt to fabricate optical composite of Li2B4O7 (LBO) and vanadium doped SrBi2Nb2O9 (SBVN) and to study its structural, dielectric, pyroelectric, ferroelectric and optical properties. Therefore the present thesis reports detailed investigations into the effect of vanadium doping on the structural and various physical properties of an n = 2 member of the Aurivillius family of oxides in the polycrystalline form and novel glass composites comprising nano/microcrystallites of this phase. Chapter 1 comprises a brief introduction to the dielectric, pyroelectric, ferroelectric and nonlinear optical properties of materials. In addition to the principles and phenomena, the material aspects of these important branches of physics are discussed. It also forms a preamble to the glasses, criteria for glass formation, glass – ceramics and subsequently ferroelectric and nonlinear optical effects that were observed in glasses and glass - ceramics. Chapter 2 describes the material fabrication techniques adopted to prepare polycrystalline and grain – oriented ceramics, glasses and glass nanocrystalcomposites. The details of various structural, dielectric, pyroelectric, ferroelectric and optical measurement techniques employed to characterize these materials are also included. Chapter 3 discloses the fabrication of strontium bismuth niobate ceramics and their characterization for dielectric and impedance properties. The dielectric properties of strontium bismuth niobate ceramics have been modeled based on Jonscher’s Universal formalism. The coefficients of the Jonscher’s expression, exponent n(T) undergoes a minimum and A(T) exhibits a peak at the Curie temperature, Tc (723K). A strong low frequency dielectric dispersion (LFDD) associated with an impedance relaxation has been found to exist in these ceramics in the temperature range 573 - 823K. The Z′′ of the AC complex impedance showed two distinct slopes in the frequency range 100Hz-1MHz suggesting the existence of two dispersion mechanisms. The exponents m and n were obtained from the curve fitting. The exponent n was found to exhibit a minimum at the Curie temperature, Tc (723K) whereas the m was temperature independent. Chapter 4 deals with the fabrication of vanadium doped SrBi2Nb2O9 ceramics and their characterization for microstructural, dielectric, pyroelectric and ferroelectric properties. The average grain size of the SrBi2Nb2O9 (SBN) ceramic containing V2O5 was found to increase with increase in V2O5 content. The dielectric constant (εr) as well as the dielectric loss (D) increased with increase in grain size (6µm-17µm). The pyroelectric coefficient was found to be positive at 300K and showed an increasing trend with increasing grain size. Interestingly, the SrBi2(Nb0.7V0.3)2O9-δ ceramics consisting of 17µm sized grains showed higher remnant polarization (Pr) and lower coercive field (Ec) than those with grains of 7µm. Chapter 5 deals with the dielectric properties which were studied in detail in the 100Hz to 1MHz frequency range at various temperatures (300 – 823 K) for undoped and vanadium (10 mol%) doped SrBi2Nb2O9 (SBVN10) ferroelectric ceramics. A strong low frequency dielectric dispersion was encountered in these ceramics in the 573 – 823 K temperature range. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonscher’s dielectric dispersion relations. The dielectric behavior of SBN and SBVN10 ceramics was rationalized using the impedance and modulus data. The electrical conductivity studies of layered SrBi2(Nb1-xVx)2O9-δ ceramics with x lying in the range 0 to 0.3 (30 mol%) were centered in the 573 – 823K temperature range as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D0) and the mean free path (a) were calculated using Rice and Roth formalism. The conductivity parameters such as ion hopping rate (ωp) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The afore mentioned microscopic parameters were found to be V2O5 content dependent in SrBi2(Nb1-xVx)2O9-δceramics. Chapter 6 describes the fabrication of partially grain – oriented SrBi2(Nb1-xVx)2O9-δ (0 ≤x≤3.0 in molar ratio) ceramics and characterization for their structural, microstructural, dielectric, pyroelectric and ferroelectric properties. The grain – orientation factor and the microstructural features were studied by XRD and scanning electron microscopy as a fuction of sintering temperature and V2O5 content. The dielectric constant measured along the direction parallel and perpendicular to the pressing axis has shown a significant anisotropy. The pyroelectric and ferroelectric properties were superior in the direction perpendicular to the pressing axis (polar) to that in the parallel direction. The fabrication and characterization details of (100 – x) (Li2B4O7) – x (SrO - Bi2O3 - 0.7 Nb2O5 – 0.3 V2O5) (10 ≤ x ≤ 60, in molar ratio) glasses and glass nanocrystal composites are dealt within Chapter 7. The nanocrystallization of strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9-δ(SBVN)) has been demonstrated in Li2B4O7 glasses. The glassy nature of the as – quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as – quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X – ray powder diffraction studies. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat – treated at 783K/6h) confirm the presence of nano rods of SBVN embedded in Li2B4O7 glass matrix. Chapter 8 presents the physical properties of the glasses and glass nanocrystal composites. Dielectric constant of both the as – quenched and glass nanocrystal composites was found to increase with increase in the composition, whereas the loss was observed to decrease with increasing SBVN composition. Different dielectric mixture formulae were employed to analyze the dielectric properties of the glass nanocrystal composite. The electrical behaviour of the glasses and glass nanocrystal composites was rationalized using impedance spectroscopy. The observed pyroelectric response and ferroelectric hysteresis of these composites confirmed the polar nature. Various optical parameters such as optical band gap (Eopt), Urbach energy (∆E), refractive index (n), optical dielectric constant (ε′∞) and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied. Transparent glasses embedded with nanocrystallites of SBVN exhibited intense second harmonic signals in transmission mode when exposed to IR laser light at λ = 1064 nm. The thesis ends with a summary of the important findings and conclusions.

published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy